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   <title>8.5.&nbsp; Number of Versions</title><link rel="stylesheet" href="css/freebsd_docbook.css" type="text/css"><meta name="generator" content="DocBook XSL-NS Stylesheets V1.75.2"><link rel="home" href="book.html" title="The Apache HBase Book"><link rel="up" href="schema.html" title="Chapter&nbsp;8.&nbsp;HBase and Schema Design"><link rel="prev" href="keysize.html" title="8.4.&nbsp;Try to minimize row and column sizes"><link rel="next" href="hbase_metrics.html" title="Chapter&nbsp;9.&nbsp;Metrics"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">8.5.&nbsp;
  Number of Versions
  </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="keysize.html">Prev</a>&nbsp;</td><th width="60%" align="center">Chapter&nbsp;8.&nbsp;HBase and Schema Design</th><td width="20%" align="right">&nbsp;<a accesskey="n" href="hbase_metrics.html">Next</a></td></tr></table><hr></div><div class="section" title="8.5.&nbsp; Number of Versions"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="schema.versions"></a>8.5.&nbsp;
  Number of Versions
  </h2></div></div></div><p>The number of row versions to store is configured per column
      family via <a class="link" href="http://hbase.apache.org/apidocs/org/apache/hadoop/hbase/HColumnDescriptor.html" target="_top">HColumnDescriptor</a>.
      The default is 3.
      This is an important parameter because as described in <a class="xref" href="datamodel.html" title="Chapter&nbsp;11.&nbsp;Data Model">Chapter&nbsp;11, <i>Data Model</i></a>
      section HBase does <span class="emphasis"><em>not</em></span> overwrite row values, but rather
      stores different values per row by time (and qualifier).  Excess versions are removed during major
      compactions.  The number of versions may need to be increased or decreased depending on application needs.
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